Continuously variable automatic transmissions (CVT) for motor vehicles customarily comprise a start-up unit, a forward and reverse drive unit, a variable speed gear, an intermediate shaft, a differential and a control unit. A CVT is ordinarily driven by an internal combustion engine, via a drive shaft, and possesses a hydraulic start-up element. The forward and reverse drive unit is used to reverse the direction of rotation for forward or reverse motion and is customarily comprised of a planetary reverse-gear mechanism.
The variable speed gear is comprised of two V-pulleys and a belt, wherein each V-pulley comprises a first pulley half that is stationary in an axial direction, and a second pulley half that can be shifted in an axial direction. The belt travels around between these two V-pulleys.
By displacing the V-pulley halves, the radius of rotation of the belt and thus the gear ratio of the transmission can be changed. The second V-pulley is non-rotatably connected to an output shaft that transfers the torque to an intermediate shaft via a pair of toothed gears. The torque from the intermediate shaft is transferred via a second pair of toothed gears to the differential.
The control and/or regulation of the CVT is customarily accomplished by way of a hydraulic control unit. The hydraulic control unit comprises electromagnetic control elements and hydraulic valves. A pump forces a pressurized fluid from a lubricant pan to a hydraulic control unit. In this the electromagnetic control elements are most frequently operated via an electronic transmission control system.
To actuate the forward and reverse drive unit shifting components are customarily used, which can be selected by way of a gear selector device. This gear selector device receives signals from the driver of the vehicle, wherein the driver may select from among the drive gears P, R, N or D, for example. The gear selector device customarily corresponds to a manual gearshift lever, with which the driver transmits the signal to the transmission. This gearshift lever most frequently is mechanically connected to a control unit. By way of this control unit, the valves for loading the shifting elements are then mechanically controlled.
This type of arrangement is described in EP 0 890 046 B1. In that system shifting components are pressurized by way of a hydraulic system. In this, the gear selected by the driver is engaged by way of a so-called selector valve, which corresponds to a hydraulic valve. In this case, the selector lever is mechanically connected directly to the selector valve.
The mechanical control for the selector valve customarily consists of a gearshift control cable, which connects the selector lever to the control unit in the transmission. The control unit is moved, via the gearshift control cable, which causes a mechanical adjustment of the selector valve. Due to the preferred positioning of the control unit on the upper side of the transmission and the positioning of the transmission control unit in the oil pan on the lower side of the transmission, the selector valve is frequently directed in a separate selector valve housing in the direct vicinity of the control unit. From this selector valve housing, a hydraulic connection to the transmission control unit is then necessary. This connection, along with the separate selector valve housing itself, is costly. Furthermore, the hydraulic connection of the selector valve housing to the transmission control unit severely limits the arrangement of the individual transmission components.
The objective of the invention is to improve upon known hydraulic control systems.
The objective is achieved with a hydraulic control device for shifting the gears of an automatic transmission, especially a continuously variable automatic transmission.